This invention relates generally to polishing equipment and, more particularly, to polishing heads and head sub-assemblies for use with semiconductor polishing equipment.
Semiconductor wafer polishing apparatus are well-known in the art and are conventionally used to planarize a semiconductor wafer in a process known as chemical-mechanical-polishing (CMP). Such polishing apparatus typically include one or more polishing heads, each of which supports a respective semiconductor wafer and positions the wafer adjacent a polishing surface, such as a polishing pad. The polishing head is moved relative to the polishing pad and a suitable polishing slurry is introduced between the wafer and the pad.
Typically, a polishing head includes a central substrate carrier which is surrounded by a substrate retainer. The substrate carrier and the substrate retainer cooperate to form a substrate-receiving pocket that prevents the substrate from moving laterally with respect to the polishing head during polishing operations. To polish the surface of a substrate, the wafer carrier is brought into contact with the polishing pad. Exposed surface layers of the substrate are removed by a combination of chemical reaction and frictional forces brought to bear upon the substrate surface. The frictional forces are created by relative movement of the polishing head and the polishing pad. For example, in one common arrangement, the polishing head is rotated about a rotational axis while the polishing pad undergoes lateral translation relative to the rotating polishing head. Both the polishing head and the polishing pad are placed in rotational motion.
During polishing operations, it is important that an adequate supply of slurry be maintained between the substrate and the polishing pad. It is of considerable importance that the wafer polishing machine be able to planarize substantially the entire exposed surface of the substrate. Difficulty often arises with respect to the marginal edge of the substrate, which can often be polished at a rate that is different than the center of the substrate. If the polishing rate at the periphery of the wafer differs excessively from the polishing rate at the center of the wafer, the periphery of the substrate may not be suitable for use in subsequent semiconductor processing stages. The edge-to-center polishing uniformity can be affected by a variance in the amount of slurry at the center of the substrate versus the periphery of the substrate. In order to provide a uniform amount of slurry between the substrate and the polishing pad, polishing equipment manufacturers have developed various techniques for delivering slurry to the polishing pad. For example, one or more nozzles can be provided within the polishing head to deliver slurry to the polishing pad.
In one method, one or more slurry nozzles are mounted near the perimeter of the polishing head and slurry is dispensed onto the polishing pad during rotation of the polishing head. Despite the application of slurry nozzles to the polishing head, non-uniform polishing of semiconductor substrates continues to be a problem in polishing operations. Accordingly, further development of the polishing equipment is necessary to provide more uniform substrate polishing.
In accordance with one aspect of the invention, a polishing apparatus includes a polishing pad and a polishing head assembly coupled to a rotatable shaft. A retainer is engaged with the head assembly such that a substrate is held against a substrate carrier mounted to the polishing head. The retainer ring has a face surface opposite the surface of the polishing table. When a polishing slurry is applied to the surface of the polishing pad, a portion of the slurry flows into the cavity such that, during operation of the polishing apparatus, slurry continuously flows from the cavity onto the polishing table. The continual release of polishing slurry from the cavity provides a uniform amount of slurry between the substrate and the polishing table during operation of the polishing apparatus.
In another aspect of the invention, a polishing head assembly is provided that includes a substrate carrier having an annular indentation at the perimeter of the substrate carrier. A substrate retainer is positioned within the annular indentation such that a face surface of the retainer is positioned opposite a polishing pad. The face surface has a cavity that is configured to cooperate with a polishing surface in contact with the face surface to provide a liquid reservoir. The substrate carrier is configured to move in relation to a polishing surface that supports a polishing slurry. The cavity retains a portion of the polishing slurry during the movement of the substrate carrier. An offset in the cavity wall permits used slurry to flow away from the substrate retainer during rotation of the head assembly.
In yet another aspect of the invention, a substrate retainer for use in a polishing apparatus includes a continuous annular member having a face surface and a perimeter surface. A cavity resides in a portion of the face surface in proximity to the perimeter surface of the annular member.
The cavity in the annular member can have several different geometric configurations, such as a hollowed-out region in the face surface, an elongated channel, and the like. Further, a plurality of cavities can reside in the face surface of the annular member in which each cavity is separated by a non-cavity containing portion of the face surface.